SiO_2基质中包埋纳米晶Si光电性质的模拟计算

采用第一性原理方法,研究了SiO2基质中包埋纳米晶Si的电子结构及光学性质。结果表明:位于约1.7eV的吸收峰是–0.59eV能级上的电子向由价键畸变产生的1.2eV能级跃迁的结果。纳米Si粒中含不饱和键的Si原子的p轨道对可见光区光的吸收有主要的贡献。同时由于这些缺陷引入的能级使价带、导带在Fermi面发生交叠而表现出导电性。     

RF磁控溅射技术制备纳米硅

利用硅-SiO2复合靶,RF磁控溅射技术制备了三种富硅量不同的SiO2薄膜,并在较大的温度范围内进行了退火。利用x射线光电子能谱,对刚淀积的样品进行了分析,结果表明三种样品都存在纳米硅粒子。使用高分辨率透射电子显微镜和电子衍射技术研究了退火后样品中纳米硅粒子析出和结晶情况,富硅量较大的两种SiO2薄膜都观测到纳米硅晶粒。统计结果表明:复合靶中硅组分从20%增加到30%,纳米硅晶粒的平均尺寸增加了15%、密度增加了2.5倍,而且随着退火温度从900℃增加到1100℃,纳米硅晶粒的平均尺寸和密度都明显增加。     

掺杂在SiO2中的ZnSe纳米晶的结构、尺寸及稳定性

利用溶胶-凝胶工艺和原位析晶技术，制备出外观透明的ZnSe纳米晶掺杂的SiO2玻璃。利用X-射线衍射研究了SiO2基质中纳米晶的相结构，根据衍射结果，利用谢乐公式计算了纳米晶的尺寸，并使用UV-Vis吸收光谱研究了纳米晶尺寸与制备工艺的关系。利用X射线光电子能谱，通过分析纳米晶中Zn，Se的化学状态研究了纳米晶的稳定性问题，结合XRD的分析结果讨论了SiO2基质对钠米晶稳定性的影响。     

高剂量离子注入直接形成Ge纳米晶的物理机理

研究了单束双能高剂量Ge离子注入、不经过退火在非晶态SiO2薄膜中直接形成镶嵌结构Ge纳米晶的物理机制.实验中利用不加磁分析器的离子注入机,采用Ge弧光放电离化自动形成的Ge+和Ge2+双电荷离子并存的单束双能离子注入方法,制备了1016～1018cm-2多种剂量Ge离子注入的Si基SiO2薄膜样品.用GIXRD表征了Ge纳米晶的存在,并仔细分析得到了纳米晶形成的阈值剂量.通过TEM分析了Ge纳米晶的深度分布和晶粒尺寸.用SRIM程序分别计算了双能离子在SiO2非晶层的射程和深度分布,与实验结合,得到纳米晶形成的物理机制,即纳米晶的形成与单束双能离子注入时Ge+和Ge2+相互碰撞产生的能量沉积在SiO2中形成的局域高温有关.     

基于锗硅异质纳米晶的非易失浮栅存储器的存储特性

利用自组织生长和选择化学刻蚀方法在超薄SiO2隧穿氧化层上制备了渐变锗硅异质纳米晶,并通过电容.电压特性和电容-时间特性研究了该纳米结构浮栅存储器的存储特性.测试结果表明,该异质纳米晶非易失浮栅存储器具有良好的空穴存储特性,这是由于渐变锗硅异质纳米晶中Ge的价带高于Si的价带形成了复合势垒,空穴有效地存储在复合势垒的Ge的一侧.     

基于锗硅异质纳米晶的非易失浮栅存储器的存储特性

利用自组织生长和选择化学刻蚀方法在超薄SiO2隧穿氧化层上制备了渐变锗硅异质纳米晶,并通过电容.电压特性和电容-时间特性研究了该纳米结构浮栅存储器的存储特性.测试结果表明,该异质纳米晶非易失浮栅存储器具有良好的空穴存储特性,这是由于渐变锗硅异质纳米晶中Ge的价带高于Si的价带形成了复合势垒,空穴有效地存储在复合势垒的Ge的一侧.     

高剂量离子注入直接形成Ge纳米晶的物理机理

研究了单束双能高剂量Ge离子注入、不经过退火在非晶态SiO2薄膜中直接形成镶嵌结构Ge纳米晶的物理机制．实验中利用不加磁分析器的离子注入机，采用Ge弧光放电离化自动形成的Ge+和Ge2+双电荷离子并存的单束双能离子注入方法，制备了1e16～1e18cm－2多种剂量Ge离子注入的Si基SiO2薄膜样品．用GIXRD表征了Ge纳米晶的存在，并仔细分析得到了纳米晶形成的阈值剂量．通过TEM分析了Ge纳米晶的深度分布和晶粒尺寸．用SRIM程序分别计算了双能离子在SiO2非晶层的射程和深度分布，与实验结合，得到纳米晶形成的物理机制，即纳米晶的形成与单束双能离子注入时Ge＋和Ge2＋相互碰撞产生的能量沉积在SiO2中形成的局域高温有关．     

4H-SiC纳米薄膜的晶化研究

采用新电极结构的PECVD技术，在高功率密度、高氢稀释比、低温、偏压及低反应气压的条件下，在SiO2玻璃表面形成双等离子流，增加了SiO2表面SiC的成核几率，增强成核作用，形成纳米晶。采用高H2等离子体刻蚀弱的、扭曲的、非晶Si-C及Si-Si和Si-H等键时，由于H等离子体对纳米SiC晶粒与非晶态键的差异刻蚀作用，产生自组织生长，发生晶化。Raman光谱和透射电子衍射（EM）的测试结果表明，纳米晶SiC是4H-SiC多型结构。实验结果指出，SiC纳米晶的形成必须经过偏压预处理成核，并且其晶化存在一个功率密度阈值；当低于这一功率密度阈值时，晶化消失；当超过这一阈值时，纳米晶含量随功率密度的提高而增加，晶粒尺寸加大。电子显微照片表明晶粒尺寸为10-28nm，形状为微柱体。随着晶化作用的加强，电导率增加，导电机理是渗流作用所致。     

Si基纳米结构的电子性质

各种Si基纳米发光材料在Si基光电子器件及其全Si光电子集成技术中具有潜在的应用前景,从理论和实验上对其电子结构进行研究,有助于我们深化对其发光机制的认识与理解。本文主要从量子限制效应发光这一角度,着重介绍了Si纳米晶粒、Ge/Si量子点,SiO2/Si超晶格和超小尺寸Si纳米团簇等不同Si基纳米结构的电子性质以及它们与发光特性之间的关系。还讨论了介质镶嵌和表面钝化对其电子结构的影响。     

激光加工形成硅基上的氧化低维纳米结构的PL发光

用激光辐照硅样品和硅锗合金样品能够形成多种氧化低维纳米结构,可以用激光与半导体相互作用产生的等离子体波模型来解释这些结构的形成机理.其中,在单晶硅上形成的网孔壁结构有很强的706nm波长的光致发光(PL)峰,在硅锗合金上形成的多孔状结构于波长为725nm处有极强的PL峰,在硅锗合金上形成的条形片状结构分别在波长为760nm和866nm处也有较强的PL峰;这些结构表面都覆盖有氧化硅层,在硅锗合金上的氧化硅层中镶嵌有纳米锗品团簇,并用相应的模型解释了这些氧化低维纳米结构的强光致发光效应.     

Electronic structure at interfaces of cubic Gd2O3 with embedded Si nanocrystals

The electronic structure of silicon nanocrystals (∼2-6 nm in size) embedded in cubic Gd₂O₃ epi-layers grown on (1 1 1) Si was analyzed using spectroscopic ellipsometry and photocharging methods. With decreasing nanocrystal size down to the 2 nm range, the optical absorption exhibits a spectacular shift in spectral threshold to 2.9 ± 0.1 eV, as compared to the 1.12 eV absorption edge of the bulk Si crystal. This shift suggests a significant influence of quantum confinement on the Si nanocrystal/oxide interface band diagram, which effect is shown to be predominantly caused by an upshift of the nanocrystal conduction band.     

Lateral photoconductivity of Ge/Si heterostructures with Ge quantum dots

The spectral dependences of the lateral photoconductivity of Ge/Si heterostructures with Ge quantum dots are studied. The photoresponse of the Ge/Si structures with Ge nanoclusters is detected in the range 1.0–1.1 eV at T = 290 K, whereas the photocurrent in the single-crystal Si substrate is found to be markedly suppressed. This result can be attributed to the effect of elastic strains induced in the structure on the optical absorption of Si. At temperatures below 120 K, the heterostructures exhibit photosensitivity in the spectral range 0.4–1.1 eV, in which the Si single crystal is transparent. The photocurrent in this range is most likely due to the transitions of holes from the ground states localized in the quantum dots to the extended states of the valence band.     

Growth of Si and Ge nanostructures on Si substrates using ultrathin SiO/sub 2/ technology

Using scanning reflection electron microscopy and a high-temperature scanning tunneling microscopy (STM), we study the growth processes of Si and Ge nanostructures on Si substrates covered with ultrathin SiO/sub 2/ films. Si windows are formed in the ultrathin SiO/sub 2/ films by irradiating focused electron beams used for SREM or field emission electron beams from STM tips before or during heating samples. Ge nanoislands are grown only at the Si window positions by depositing Ge on the samples and by subsequent annealing of them. Moreover, Ge nanoislands about 7 nm in size and ultrahigh density (>10/sup 12//cm/sup 2/) are grown on the ultrathin SiO/sub 2/ films. These nanoislands can be manipulated by STM when they are separated from Si substrates by the ultrathin SiO/sub 2/ films. Si, Ge, Ge/Si and Si/Ge/Si nanoislands can also be grown on the Si windows by selective growth using Si/sub 2/H/sub 6/ and GeH/sub 4/ gases. These nanoislands are found to be stable on the Si windows during high-temperature annealing. These results indicate that ultrathin SiO/sub 2/ technology is useful for growing Si and Ge nanostructures on given areas.     

Growth and Luminescence of Polytypic InP on Epitaxial Graphene

Van der Waals epitaxy is an attractive alternative to direct heteroepitaxy where the forced coherency at the interface cannot sustain large differences in lattice parameters and thermal expansion coefficients between the substrate and the epilayer. Herein, the growth of monocrystalline InP on Ge and SiO₂/Si substrates using graphene as an interfacial layer is demonstrated. Micrometer‐sized InP crystals are found to grow with interfaces of high crystalline quality and with different degrees of coalescence depending on the growth conditions. Some InP crystals exhibit a polytypic structure, consisting of alternating zinc‐blende and wurtzite phases, forming a type‐II homojunction with well (barrier) width of about 10 nm. The optical properties, investigated using room temperature nano‐cathodoluminescence, indicate the signatures of the direct optical transitions at 1.34 eV across the gap of the zinc‐blende phase and the indirect transitions at ≈ 1.31 eV originating from the alternating zinc‐blende and wurtzite phases. Additionally, the InP nanorods, found growing mainly on the graphene/SiO₂/Si substrate, show optical transition across the gap of the wurtzite phase at ≈ 1.42 eV. This demonstration of InP growth on graphene and the correlative study between the structure and optical properties pave the way to develop hybrid structures for potential applications in integrated photonic and optoelectronic devices.     

硅缓冲层提高选区外延生长硅基锗薄膜质量

研究了Si缓冲层对选区外延Si基Ge薄膜的晶体质量的影响。利用超高真空化学气相沉积系统,结合低温Ge缓冲层和选区外延技术,通过插入Si缓冲层,在Si/SiO_2图形衬底上选择性外延生长Ge薄膜。采用X射线衍射(XRD)、扫描电子显微镜(SEM)、原子力显微镜(AFM)表征了Ge薄膜的晶体质量和表面形貌。测试结果表明,选区外延Ge薄膜的晶体质量比无图形衬底外延得到薄膜的晶体质量要高;选区外延Ge薄膜前插入Si缓冲层得到Ge薄膜具有较低的XRD曲线半高宽以及表面粗糙度,位错密度低至5.9×10~5/cm^2,且薄膜经过高低温循环退火后,XRD曲线半高宽和位错密度进一步降低。通过插入Si缓冲层可提高选区外延Si基Ge薄膜的晶体质量,该技术有望应用于Si基光电集成。     

硅、锗和氩离子注入富硅二氧化硅的电致发光

将Si、Ge和Ar三种离子注入到磁控溅射制备的富硅二氧化硅和热生长的二氧化硅中,在N2气氛中,作550、650、750、850、950和1050℃退火后,进行电致发光研究.对比样品为退火条件相同的未经注入的上述两种二氧化硅.对于离子注入情况,只观察到Au/1050℃退火的离子注入的富硅二氧化硅/p-Si的电致发光.低于1050℃退火的离子注入富硅二氧化硅和上述各种温度下退火的热生长二氧化硅,无论离子注入与否,都未观察到电致发光.Au/未注入富硅二氧化硅/p-Si的电致发光光谱在1.8eV处出现主峰,在2.4eV处还有一肩峰.在Au/Si注入富硅二氧化硅/p-Si的电致发光谱中,上述两峰的     

Lateral photoconductivity of multilayer Ge/Si structures with Ge quantum dots

Spectra of lateral photoconductivity of multilayer Ge/Si structures with Ge quantum dots, fabricated by molecular-beam epitaxy are studied. The photoresponse caused by optical transitions between hole levels of quantum dots and Si electronic states was observed in the energy range of 1.1–0.3 eV at T = 78 K. It was shown that the electronic states localized in the region of Si band bending near the Ge/Si interface mainly contribute to lateral photoconductivity. The use of the quantum box model for describing hole levels of quantum dots made it possible to understand the origin of peaks observed in the photoconductivity spectra. A detailed energy-level diagram of hole levels of quantum dots and optical transitions in Ge/Si structures with strained Ge quantum dots was constructed.     

单原子层应变超晶格(Si)_1/(Si_(1-x)Ge_x)_1(100)的电子结构

在计入应力的紧束缚框架之下计算了单原子层应变超晶格(Si)_1/(Si_1-xGo_x)_1的电子结构.对应于不同应变条件,得出能隙随组分的变化,并结合能带边不连续的变动加以考察.超晶格取Si(或Ge)晶格常数后能隙随组分的非单调变化源自合金受相同应力后能隙的类似特点.超晶格能带及态密度均呈现类Si的闪锌矿结构对称性.在虚晶近似得出的能隙和电子状态密度的基础上,利用相干势近似作了进一步的修正.     

Properties of Si/sub 3/N/sub 4//Si/sub x/Ge/sub 1-x/ metal-insulator-semiconductor capacitors

The density of fast interface states was studied in Si/sub 3/N/sub 4//Si/sub 0.8/Ge/sub 0.2/ metal-insulator-semiconductor (MIS) capacitors. The interface state density does not appear to be strongly affected by the presence of a thin Si interlayer between the nitride and SiGe alloy. This is in contrast to the results when SiO/sub 2/ is used as the insulator material in similar structures.<>